Slide-fit nuts, sometimes referred to as jam nuts, are generally known in the art for rapid push-on mounting onto a threaded bolt, stud or similar threaded structure, wherein the nut is installed onto the bolt to a seated or nearly seated position with little or no rotational motion. Such slide-fit nuts are typically constructed to include a plurality of part-cylindrical, separate nut segments which are mounted in a cylindrical array within an outer nut casing or housing. The nut segments are internally threaded to collectively define a spiral female thread for engaging a mating male thread on an associated bolt. One or more springs engage the nut segments to apply a radially inward force urging the nut segments into normal threaded engagement with the male thread. However, cam surfaces cooperating between the outer nut casing and the nut segments aid the movement of the segments to a disengaged relation to permit the nut segments to displace radially outwardly when the nut is pushed in one axial direction over the bolt. Accordingly, the slide-fit nut can be displaced rapidly over the axial length of the bolt, with a non-rotational push-on action, to a seated position in abutment with a substrate surface defined by an element which is to be held in place by the nut. If further tightening of the nut is desired, a small amount of nut rotation, to advance the nut along the male thread, can be accomplished by engaging the nut casing with a wrench or the like. For examples of push-on nuts of this general type, see U.S. Pat. Nos. 4,378,187 and 5,139,381.
While push-on nuts beneficially permit rapid nut mounting without requiring substantial nut rotation over the protruding free length of a bolt, some nuts which have been made available in the art have not permitted a similarly rapid pull-off removal from the bolt when disassembly is desired. Instead, it has been necessary to back-rotate the nut from the seated position, with such back-rotation continuing for the entire free length of the bolt until the nut is removed. In some applications, this requirement for rotational nut displacement for removal purposes can be undesirably time consuming and tedious.
Other push-on nuts described in the art have attempted to permit a pull-off removal, but have not been successful. Such nuts have not properly stayed in position under axial load. For an example of a push-on, pull-off nut, see U.S. Pat. No. 5,139,381. In that nut arrangement, a two-part cam system is used to move the nut's female thread segments into and out of engaged position. At the upper end of the nut housing, the end cap of the housing is fitted with ridges which mate with slots in the upper ends of the nut segments. Radial turning of the nut housing results in either engagement or disengagement of the nut segments from the male thread. At the lower end of the nut housing, the lower portion of the inner housing wall is angled inwardly, so that under an upward axial load, a resultant horizontal inward force keeps the nut segments in the engaged position. However, if the slope is shallow, equal to or less than the angle on the thread of the male member, under an upward axial load, such as the load imparted on the nut in its secured (fastened) state, the threaded nut segments can be forced outward by the threaded bolt, disengaging the threads, resulting in the full upward load being held by only the upper threads of the nut segments. These upper threads may remain partially engaged due to the cam ridges in the end cap which move the nut segments. Such condition often results in failure of the nut, as full load on a portion of the threads strips the threads, either on the nut segments or on the bolt. When the angle at the lower end of the nut housing is increased, the same upward axial force produces a greater inward force, keeping the nut segments in place and engaged with the threaded bolt over the length of the segments. However, this increased force reduces the ability to axially pull-off the nut.
Another shortcoming of the nut device shown in U.S. Pat. No. 5,139,381 is the lack of cooperation between the fastener segments. Proper operation of such a nut requires that the fastener segments contract into their engaged positions, in a uniform, synchronous manner. If the segments engage and disengage independently rather than in unison, the fastener may not fully disengage the threaded member, or when engaging, may not properly align with the threaded member. In the nut arrangement shown in that patent, the segment end faces which extend along the thread axis are linear, planar faces, which allow the segments to slip radially with respect to each other, provide no alignment or guidance, and do not act to keep the segments in positional coordination with each other in a generally circular pattern.
There exists, therefore, a significant need for an improved slide-fit fastener which can be mounted onto a bolt quickly and easily with simple push-on action, which will maintain threaded engagement along the length of the fastener under axial load, i.e., when the fastener is performing a fastening function, whose nut segments are configured to be self-aligning, and which is adapted for rapid removal from the bolt with a simple pull-off action. The present invention fulfills these needs and provides further related advantages.